1. Field of the Invention
The present invention relates to nanowires including metal nanodots and a method for producing the nanowires. More particularly, the present invention relates to a new structure of nanowire including a plurality of metal nanodots uniformly disposed therein, and a method for producing the nanowires.
2. Description of the Related Art
Nanowires are linear materials whose diameter is in the nanometer range (1 nm=10−9 m) and whose length is greater than the diameter. Nanowires can have a length on the order of several hundred nanometers, micrometers (1 μm=10−6 m), or millimeters (1 mm=10−3 m). Nanowires exhibit various physical properties depending on their diameter and length.
Extensive research on the production and physical properties of nanoparticles is now being actively undertaken, but fewer studies on methods for producing nanowires have been reported. Representative methods for producing nanowires include the template approach, chemical vapor deposition (CVD), laser ablation, and the like.
According to the template approach, pores having a size of a few to several hundred nanometers are used as templates to produce nanowires. In one example, an aluminum electrode is first oxidized to form aluminum oxide on the surface of the electrode, and then the aluminum oxide is electrochemically etched to form nanoscale pores. The resulting structure is dipped in a solution containing metal ions. When electricity is applied to the solution, the metal ions accumulate on the aluminum electrode through the pores, until the pores are filled with the metal ions. Thereafter, the oxide is removed by appropriate treatment to leave metal nanowires behind.
However, since the template approach is a laboratory method and can be complicated and time-consuming to implement, it is not ideal for mass production of nanowires. The diameter and length of the nanowires depend on the size and depth of the pores, and it can be very difficult to form pores having a size on the order of a few nanometers and a depth ranging from a few hundred micrometers to a few millimeters. Therefore, the template approach is limited in that it is very difficult to produce nanowires having a diameter of a few nanometers.
With chemical vapor deposition (CVD), a raw material gas containing a desired material is fed into a reactor and decomposed (e.g., by heat or plasma energy) within the reactor. A substrate is exposed to the desired material to form nanotubes or nanowires thereon. Such chemical vapor deposition methods are divided into low-pressure chemical vapor deposition (LPCVD), atmospheric-pressure chemical vapor deposition (APCVD) and high-pressure chemical vapor deposition (HPCVD) based on the inner pressure of the reactor.
One type of CVD method is plasma-enhanced chemical vapor deposition (PECVD), which makes use of a relatively low temperature plasma to form the nanomaterials. For example, carbon nanotubes or nanowires can be produced by using a hydrocarbon gas (e.g., methane) as a raw material gas and dispersing transition metal nanoparticles (e.g., nickel, cobalt and iron particles) on a glass substrate. It is necessary to form a transition metal thin film before growth of the carbon nanotubes or nanowires. The transition metal acts as a catalyst for decomposing the raw material gas and a nucleation site for the formation of the nanotubes or nanowires. Many nanomaterials are produced and grown on wafers in this fashion.
Laser ablation can be used to produce monolayers of carbon nanotubes and semiconductor nanowires. Laser ablation has advantages over other production methods in that nanomaterials can be produced with high purity or are easily purified. In one example, a transition metal and a basic bulk material for producing nanomaterials are mixed in a predetermined ratio to prepare a specimen. The specimen is then placed inside a quartz tube, and evaporated using an externally applied laser to produce the nanotubes or nanowires. Argon is commonly used as a buffer gas. The nanotubes or nanowires thus prepared and the buffer gas are transferred and attached to or around a cooled collector.
The nanowires produced by these methods can be used in electronic devices, such as field effect transistors (FETs), sensors, photodetectors, and the like. In addition, nanowires containing metal nanodots can be used as waveguides utilizing optical coupling of the metal nanodots or can be use in highly photosensitive detectors for cell diagnosis in the field of biotechnology. In addition, such nanowires could be applied to metal base transistors having a metal-silicon-metal structure and devices with newly added functions.
A few methods for producing nanowires comprising metal nanodots are known. For example, gold atoms can be deposited on the surface of grown nanowires and then introduced inside the nanowires. One example of such a method is schematically shown in FIG. 4. According to this method, however, all of the gold (Au) atoms or nanodots cannot be introduced into the nanowires. Furthermore, the positions of the gold atoms or nanodots attached on the surface of the nanowires are not controlled, and are instead randomly distributed. Therefore, the method has disadvantages in that the gold atoms cannot be uniformly disposed within the nanowires and it is difficult to control the size of the gold atoms.